Invisible blood in urine may be an early warning sign of bladder cancer, new research claims.

Scientists at the University of Exeter say they found that one in 60 people over the age of 60 who had invisible blood in their urine developed bladder cancer. The figure was around half those who had visible blood in their urine – the best known indicator of bladder cancer.

In a statement, Sarah Price, the study's lead author, said, "It is well known that if you see blood in your urine you should contact your GP (general practitioner), who is likely to refer you for tests. But there is no clear guidance for GPs on what to do if they detect blood that is not visible during routine tests.

"The three-quarters of patients who are diagnosed early have much better outcomes than those whose disease is diagnosed late. Anything we can do to boost early detection is crucial to help save lives," she added.

The study examined more than 26,000 people and the team found that the risk of bladder cancer was 1.6% in people over 60 who had invisible blood in their urine.

The study was published in the British Journal of General Practice Monday.